The following relates to phased arrays of radio frequency (RF) coils for magnetic resonance imaging, and will be described with particular reference thereto. It finds application more generally in conjunction with magnetic resonance imaging, magnetic resonance spectroscopy, and other magnetic resonance applications.
Many techniques increasingly employ arrays of surface coils to act as a transmit and receive antenna. Each surface coil of the array typically includes a conductive RF loop, and required electronic components providing required features including frequency tuning the magnetic resonance frequency and matching to required impedance (e.g. 50 ohm); a pre-amplifier for amplifying the received signal from the subject in the magnet; coil detuning during the transmit phase; coil decoupling from adjacent and non-adjacent coil elements of the phased array coils. The required electronics are typically positioned close to the conductive RF loop.
Normally, each element of the phased array coil includes the conductive coil loop, a preamplifier decoupling network and a preamplifier, typically the preamplifier includes a transistor amplifier preceded by conditioning circuit.
The standard preamplifier decoupling network consists of capacitors and inductors which form a parallel resonant circuit with the conditioning circuit of the preamplifier and the output capacitor of the coil loop and blocks current from flowing in the surface coil. This circuit de-couples the coil elements, especially non-adjacent elements. As is well known, adjacent coil elements are typically de-coupled by different methods, including geometry, capacitive, and inductive de-coupling, but it is not always possible to de-couple by these methods therefore the parallel resonant circuit with lower input impedance preamplifier in each coil is necessary to de-couple from non-adjacent coils of the array.
However, using the traditional decoupling techniques of the prior art, either a good impedance matching with the pre-amplifier or a good decoupling (high decoupling impedance) may be achieved. However, simultaneous improvement of both of these parameters is very difficult and often impossible to obtain. Thus improvement in one comes generally at a deterioration in the other leading to unacceptable design compromises to obtain the best SNR available.